In cellular radio systems the mobile radio stations, i.e. subscriber terminals, may roam from one cell to another within the area of the cellular network. A cellular radio network usually keeps files on the location of a mobile station with an accuracy of a so-called location area. Cellular radio networks employ a fixed location area configuration: each location area permanently consists of the same cells and their base stations. The location area information broadcast by a base station informs a mobile station of the location area to which the base station belongs. When the mobile station moves to another cell within the same location area, location updating to the cellular radio network is not needed. However, when the mobile station, on the basis of the location area information, observes that the location area changes with the new base station, it starts location updating by sending a location updating request to the cellular radio network. As a result of this location updating request, the cellular radio network stores the new location area of the mobile station as location data in the subscriber database.
As the location of a mobile station is known only with an accuracy of a location area, the mobile station must be paged in all radio cells belonging to this location area, e.g. for the establishment of an in-coming call. This results in a considerable signalling load in the radio network between the exchange and the base stations and also on the radio path. On the other hand, to reduce the size of a location area in order to avoid the above-mentioned drawback leads to the fact that a mobile station changes location areas more frequently, whereby the location updating frequency and the signalling caused by it increase. At present the tendency is towards larger location areas with the aim of reducing the location updating frequency.